The different stimuli must be assigned at the net or pin level as you intend to use them. If you assign a stimulus to a net, then whatever pin is the driver on that net uses that stimulus unless overridden with a pin-level stimulus assignment. It sounds like you assigned stimulus patterns at the pin level, so the other drivers on the net use the default stimulus.
Thanks for clearing up the difference, however this does not seem to be the problem.
The stimulus patterns being set on the nets are causing me the problems. I have set either stimulus at net OR stimulus at pin(clearing to default before changing where I stimulate signals), not both, so I do not think I can be overridding the net stimulus.
Just to be clear, D1, D2 & D3 are all seperate nets, with seperate drivers.
Is there another reason that D2 & D3 appear the same as D1?